The wire bonding machine is but one example of many kinds of apparatus in which the position of an element in a plane is altered as a consequence of remotely developed motion or position signals. In its broader sense, this invention has general application in this field. However, the invention has a special meaning in the wire bonding machine field where it provides a new approach and a very practical solution to some long standing problems.
In a typical application, a wire bonding machine may be used to interconnect micro circuit points which are separated by distances from less than one millimeter up to about five millimeters using wires in the order of twenty-five micrometers diameter (0.001 inch). Those distances are too small to discern with the unaided eye. High powered stereo microscopes are used in which the field of view at the work plane may be only five millimeters in diameter. Obviously such small dimensions do not permit direct manipulation of position of work piece and bonding tool. Much of the manipulation is done by hand. Even in an automated bonding sequence initial orientation is accomplished manually.
Two different approaches have been utilized to provide remote, amplified, positioning capability to the bonding machine operator. One approach employs a mechanical pantograph such, for example, as the micro manipulator described in U.S. Pat. No. 3,474,685 to Miller. Movement of the manipulator handle of a very accurate pantograph is reproduced in movement of the work piece or the tool. The field of movement of the micro manipulator input handle corresponds exactly to the field of relative movement of the work piece and bonding tool. Thus, when the input handle is in the center of its field of movement, the work piece (or bonding tool) is in the center of its field of movement. When the input handle is at one edge of its field of movement, the work piece (or bonding tool) will be positioned at the corresponding edge of its field of movement. In some applications that micro manipulator cannot be beat but it does have limitations. As the division of movement is increased to accommodate smaller work pieces and work dimensions, the field of input handle movement must be increased. Accuracy and speed suffer as the field approaches the limit of operator finger and wrist movement. Further, the all-mechanical positioner is sometimes difficult to integrate with automatic positioners.
The second approach to positioning seeks to overcome the limitations of the all mechanical system by substituting time for distance as an input parameter. The usual apparatus employs a pair of stepping motors which rotate lead screws to move the work piece (occasionally the tool) in the X and Y directions, respectively, of the work plane. The stepping motor responds to electric switch operation and it turns the lead screw at some number of steps per unit of switch closed time. Two switches are employed, one for the X direction and one for the Y direction. There are mechanical arrangements for actuating two switches with one handle to permit movement in X and Y, simultaneously. That makes movement at forty-five degrees possible so that the work piece can be moved in X or Y or at forty-five degrees to X or Y. It is possible to change the ratio of steps per unit time to achieve movement at different rates and therefor at different specific angles, but that is neither practical nor is it capable of overcoming either of two major problems with the degree-of-movement-as-a-function-of-time approach to work piece positioning.
Positioning-as-a-function-of-change-of-position permits direct movement from one point to another along any path without limitation to X and Y and an intermediate angle two and it permits continuously variable rate of change of position. The problem with that approach is that the field of input movement must be an enlarged version of the whole field of work piece movement. That problem is solved in the positioning-as-a-function-of-time approach but the solution is gained at the expense of direct, continuously variable rate of change positioning. This invention makes it possible to combine the advantages of both systems in a single system and to do it at minimum expense in reliable form without any loss of accuracy, but with increased speed and accuracy.